It is known that radioactive substances (such as for example contaminated wastes or products) have to be stored in pool type, water-filled reservoirs having bottom and side walls and an open top. The water in these reservoirs (which acts as a screen against the ionizing radiations from the said radioactive substances) has to undergo heat exchanges designed to cool the water as well as ion exchanges designed to keep the level of activity of the water low enough to be compatible with the environment. Until now, such exchanges were being carried out in exchangers situated outside the reservoirs.
Such a system (exchanger out of the reservoir) presents the advantage of enabling the use of highly performing sophisticated exchange devices; on the other hand, it has many disadvantages. For example, for cooling the water of the storage reservoir, a pumping installation is generally used to pump in continually the reservoir water and to send it, under high pressure, over a range of plate exchangers supplied under reflux by a high speed flow of cold water; the cooled water, having passed through the range of exchangers, is sent back to the reservoir. Consequently, if highly performing exchangers are used in this system, with use, an increase in the radioactivity of the exchanger is noted, as well as increasing difficulties in the maintenance of the installation. This rapid increase in radioactivity is due to the fact that the water in the reservoirs still contains in suspension colloidal radioactive particles which deposit over the entire piping and exchanging assembly situated outside the pool; therefore it becomes necessary to shield those parts of the installation which have become radioactive. The maintenance problem is due also to the fact that the exchangers used are of light construction, requiring frequent repairs which become rapidly difficult due to the high degree of contamination of the materials.